diy solar

diy solar

Growatt and 3 12v 30ah AGMs?

rykelo

New Member
Joined
Sep 3, 2021
Messages
38
Hey Guys,

Is it possible for me to use 3 x 12v 30ah AGM batteries with my 24v SPF 3000 LVM Growatt inverter? The Growatt is hooked up to 3 x 440W panels in 3S (inverter couldn't handle 3P at peak sun), off grid.

I am unclear on how I would get BMS communication between the AGMs and the Growatt. The Growatt came with a BMS cable but I don't know what it would plug into in order to connect to the AGMs.

Thanks in advance!

Ryan
 
Hey Guys,

Is it possible for me to use 3 x 12v 30ah AGM batteries with my 24v SPF 3000 LVM Growatt inverter?
No, you can use 2 in series OR 4 in series/parallel, but there's no way to make it work with 3 batteries. Also remember that an AGM is a flavor of lead acid and should only be used to 50% DoD, or 15Ah @ 24v which is 360Wh. That Growatt draws about 50-60w an hour just to exist which will kill your batteries in about 7 hours. You'll need 1200Wh a day to keep it running and working which would be 50Ah, which would be 100Ah of lead acid flavored batteries @ 24v (so 2x 100Ah AGM's or FLA's or GEL's per day).
The Growatt is hooked up to 3 x 440W panels in 3S (inverter couldn't handle 3P at peak sun), off grid.
I'm thinking you have that backwards. In Series the voltage adds up and the amperage stays the same, in Parallel it stays the same and the amperage adds up. Parallel would be 1/3 the VoC going in.
I am unclear on how I would get BMS communication between the AGMs and the Growatt. The Growatt came with a BMS cable but I don't know what it would plug into in order to connect to the AGMs.
AGM's don't have a BMS. The BMS is the little unit inside a lithium battery that keeps the cells all playing nicely with each other.

Thanks in advance!

Ryan
Sorry to give you bad news right out the gate. :(
 
Rednettek is correct. I just want to add, if you want to use small batteries, get a small inverter. You have a rather large inverter, so you need some big (much bigger) batteries.

Do you plan to use this system daily, or is it only for emergencies?
 
@Rednecktek thanks for the thorough reply I really appreciate it, and it's a huge help :) So maybe I can boot up the Growatt with just 2 of the AGMs and set the low voltage cutoff to 50% to protect the batts?

@DThames I have a 4kwh LiFeP04 that isn't holding a charge (dies overnight) and will be going in for service. During this time, I won't have a battery but would still like to be able to get some solar power during the day if there's sun.

Thanks again!
 
@Rednecktek thanks for the thorough reply I really appreciate it, and it's a huge help :) So maybe I can boot up the Growatt with just 2 of the AGMs and set the low voltage cutoff to 50% to protect the batts?

@DThames I have a 4kwh LiFeP04 that isn't holding a charge (dies overnight) and will be going in for service. During this time, I won't have a battery but would still like to be able to get some solar power during the day if there's sun.

Thanks again!
If you are trying to somehow limp along while your big battery is out of service, sure with 2 in series it could be turned on and used to some extent with the sun shining. I would turn it off overnight, because it will soon drain the batteries if on and it would be nice to start the day with more than zero power.
 
If you are trying to somehow limp along while your big battery is out of service, sure with 2 in series it could be turned on and used to some extent with the sun shining. I would turn it off overnight, because it will soon drain the batteries if on and it would be nice to start the day with more than zero power.
Yep I'm in for some limping! When you say "turn off" do you mean at the power switch or should I disconnect the batteries altogether? I've noticed that "turning off" the Growatt at the power switch stops it from producing AC but it remains on if there's solar. Then it powers off once the sun sets (or the battery dies).
 
Yep I'm in for some limping! When you say "turn off" do you mean at the power switch or should I disconnect the batteries altogether? I've noticed that "turning off" the Growatt at the power switch stops it from producing AC but it remains on if there's solar. Then it powers off once the sun sets (or the battery dies).
I mean, turn of the inverter so it is has no output. The display will go to sleep, like you said after the PV output is zero. On mine, at first light they come on and start trying to charge with what little power is available before the sun is actually on the panels. If you have power in the batteries at that point, you can decide what to do but as previously stated, it is drawn just to have them on so until the sun can produce the 50-60watts for idle power, I would just leave it off unless really needed.
 
@Rednecktek thanks for the thorough reply I really appreciate it, and it's a huge help :) So maybe I can boot up the Growatt with just 2 of the AGMs and set the low voltage cutoff to 50% to protect the batts?
Even easier, the Growatt comes pre-programmed to cut off at a low battery voltage which should correspond with what your batteries want. Just set the Growatt to AGM in the Battery Type setting and it should take care of itself.

Don’t forget to adjust your battery charging parameters. If you charge those tiny ones like a adult you will ruin them quickly. Fire could result.
Definitely this! I don't know off the top of my head what the exact setting is, but (IIRC) you want your charge rate to be limited at 0.2 * $Ah-Rating, or in your case 0.2*30Ah=6a per battery, so 12a max charging rate. If you try to pump more than that in you could blow up SWELL UP your batteries in a bad way.

You'll need to reset all that back when you get your LFP back and get the AGM's out of the loop.

*Edit: Thesaurus fail.
 
Last edited:
Don’t forget to adjust your battery charging parameters. If you charge those tiny ones like a adult you will ruin them quickly. Fire could result.
Thanks for the reminder! This scares me a bit. It sounds to me like running a 24v Growatt with 12v batteries is just a bad idea in general, probably best to just wait until the big battery is back in business.
 
Thanks for the reminder! This scares me a bit. It sounds to me like running a 24v Growatt with 12v batteries is just a bad idea in general, probably best to just wait until the big battery is back in business.
Nah, running it from a pair of 12v batteries is fine. Running it from a pair of TINY 12v batteries is the issue. :)

It's plenty to boot it up, plug in the laptop, and get all your settings configured for the big battery, you just don't really have enough Oomph! in those little guys to do much more than that.
 
Thanks for the reminder! This scares me a bit. It sounds to me like running a 24v Growatt with 12v batteries is just a bad idea in general, probably best to just wait until the big battery is back in business.
There is a max charge setting that you can set down to 10amp or so, and if you get 600+ watts of solar you can be charging and running some low powered loads without issue. If you are not really sure about messing with all of the settings, yes maybe just let it be until your main battery is back.
 
There is a max charge setting that you can set down to 10amp or so, and if you get 600+ watts of solar you can be charging and running some low powered loads without issue. If you are not really sure about messing with all of the settings, yes maybe just let it be until your main battery is back.
Thanks ya I think I'll just sit tight until the big boy is back - didn't realize I was in "things might blow up or light on fire" territory, and I certainly don't know enough not to be a danger to myself and my shed :p
 
Thanks ya I think I'll just sit tight until the big boy is back - didn't realize I was in "things might blow up or light on fire" territory, and I certainly don't know enough not to be a danger to myself and my shed :p
Agm,s don't "blow up" but if seriously misused, they can bulge, or burst, leaking acid and making a mess... if sparks are present when it happens, there can be a small poof flame... but nothing dangerous. Keep them in a plastic vented cabinet, and you are fine.
I'd do it if I was without solar for an undisclosed time waiting on service.

Simple answer is, don't abuse them.
Agm handle lfp settings fine. Just don't leave it on overnight, deep discharge hurts even agms...
 
Back
Top